First of all, this ...
is not a constant.
For constant folding (optimization at compile time) to happen, you need a a prototype of () , to make sure the result doesn't depend on input.
Otherwise arguments are allowed, which is biting you here!
The following demos with B::Deparse will demonstrate what is happening
C:\tmp>perl -MO=Deparse,-p -e"sub ten {10}; print ten() - 1"
sub ten {
10;
}
print((ten() - 1)); # <--
+- call no args
-e syntax OK
C:\tmp>perl -MO=Deparse,-p -e"sub ten {10}; print ten - 1"
sub ten {
10;
}
print(ten((-1))); # <--
+- call with args
-e syntax OK
C:\tmp>perl -MO=Deparse,-p -e"sub ten() {10}; print ten - 1"
sub ten () {
10;
}
print(9); # <--
+- constant folding
-e syntax OK
C:\tmp>perl -MO=Deparse,-p -e"sub ten {10}; 9 .. ten - 1"
sub ten {
10;
}
(9 .. ten((-1))); # <--
+- not what you wanted
-e syntax OK
C:\tmp>
updates
s/code folding/constant folding/g
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